Spin equilibrium with or without gravitational wave emission: The case of XTE J1814-338 and SAX J1808.4-3658

Abstract

In this Letter we present a new analysis of the torques acting on the accreting millisecond X-ray pulsars SAX J1808.4-3658 and XTE J1814-338, and show how our results can be used to constrain theoretical models of the spin evolution. In particular, we find upper limits on any spin-up/down phase of XTE J1814-338 of |v̇| ≲ 1.5 × 10-14 Hz s-1 at 95% confidence level. We examine the possibility that a gravitational wave torque may be acting in these systems and suggest that a more likely scenario is that both systems are close to spin equilibrium, as set by the disk/magnetosphere interaction. © 2011. The American Astronomical Society. All rights reserved.